Update sign.rs (#304)

* Update sign.rs

The absence of `use ethers_core::rand::thread_rng;` throws an error. Also, I decided to comment on examples since it's targeted at beginners.

* chore: improve language on signing docs

Co-authored-by: Georgios Konstantopoulos <me@gakonst.com>

ethers/examples/sign.rs

@@ -1,18 +1,25 @@
+// use the anyhow crate for easy idiomatic error handling
 use anyhow::Result;
-use ethers::prelude::*;
+// use the ethers_core rand for rng
+use ethers_core::rand::thread_rng;
+// use the ethers_signers crate to manage LocalWallet and Signer
+use ethers_signers::{LocalWallet, Signer};
 
+// Use the `tokio::main` macro for using async on the main function
 #[tokio::main]
 async fn main() -> Result<()> {
+    // Generate a random wallet
+    let wallet = LocalWallet::new(&mut thread_rng());
+    
+    // Declare the message you want to sign.
     let message = "Some data";
-    let wallet = LocalWallet::new(&mut rand::thread_rng());
 
-    // sign a message
+    // sign message from your wallet and print out signature produced.
     let signature = wallet.sign_message(message).await?;
     println!("Produced signature {}", signature);
 
-    // verify the signature
+    // verify the signature produced from your wallet.
     signature.verify(message, wallet.address()).unwrap();
-
     println!("Verified signature produced by {:?}!", wallet.address());
 
     Ok(())